The gas and oil exploration or production processes, in particular the SAGD processes often require a precise knowledge of the temperatures that exist in an oil well. In light of the extremely flammable nature of the environment existing in a gas/oil well, optical fibers are used to provide temperature measurements. Typically, an optical fiber based temperature sensor has an optical fiber that establishes an optical path. Gratings are formed at spaced apart intervals along that path. When the optical fiber undergoes expansion or contraction resulting from temperature changes, the optical properties of the gratings are altered. The optical properties can be measured by sending in the optical fiber an interrogation signal and then reading the responses of the individual gratings. A temperature measurement can be derived on the basis of those responses.
A challenge in this type of measurement setups is to lay the optical fiber in the well in a way to minimize any tension or bending strains. Since a tension will have the same effect on a grating as temperature does, namely alter the optical properties of the grating, any artificial tension that is not due to temperature will induce an error in the temperature measurement.
Accordingly, there is a need in the industry to develop new sensors for temperature measurements that use optical fibers and that are protected against deleterious effects of tension/bending strains that may arise during installation of the sensor or during use thereof.